The present invention relates to mixtures for the production of organic-inorganic hybrid materials and to the use thereof.
By synthesising organic-inorganic hybrid materials, attempts are made to combine properties which are typical of inorganic and organic substances in one material. Thus, as is known, glass and ceramics are characterised by their hardness and brittleness, whereas organic polymers are flexible but at the same time are also considerably softer than the aforementioned substances. Meanwhile, very many organic-inorganic hybrid materials have become known which are considerably harder than organic polymers are but which nevertheless do not exhibit the brittleness of purely inorganic materials.
Hybrid materials are classified into different types depending on the type of interaction between the inorganic and the organic component. A review on this topic is given in J. Mater. Chem. 6 (1996) 511.
One class of hybrid materials is obtained by the reaction of a homogeneous mixture of an organic polymer with metal alkoxides, e.g. Si(OEt).sub.4 or CH.sub.3 -Si(OEt).sub.3, with water. After hydrolysis and condensation of the alkoxides, an inorganic network is obtained which is penetrated by the organic polymer ("interpenetrating network"). There is no covalent chemical bonding of the polymer to the inorganic phase. Examples of hybrid materials such as these are given in U.S. Pat. No. 5,346,939 and WO 93/01226.
According to Poly. Mater. Sci. Eng. 74 (1996) 65, the compatibility of the inorganic phase with strongly polar polymers such as polyamides, polyimides, polyamide-imides or polycarbonates is particularly good. With polymers which are less polar, however, e.g. polyvinyl chlorides or polymethyl methacrylates, which are extraordinarily important in industry, phase separation often occurs, i.e. heterogeneous, turbid materials are formed. The addition of polyoxazolines has been proposed in order to improve the compatibility in systems such as these.
Another class of materials is produced similarly, but contains reactive groups, e.g. Si(OEt).sub.3 groups, in the organic polymer which is used, which reactive groups effect covalent chemical bonding to the inorganic network. Examples thereof are given in ACS Symp. Ser. 585 (1995)125, Adv. Mater. 6 (1994) 372 and in Mater. Lett. 13 (1992) 261.
"Polymeric composites" which consist of an organic polymer and of an inorganic, glassy polymer are described in WO 93/01226. It is stated to be a characteristic of these materials that the organic polymer cannot be extracted and that no glass transition point or melting point is observed.
Mixtures consisting of unreactive, thermoplastic polymers with liquid organometallic compounds are known from U.S. Pat. No. 5,346,939. In the presence of water, composite materials are obtained therefrom in which there is no mixing at a molecular level, but in which the organic and inorganic phases are separate. Composite materials such as these are turbid, and are therefore unsuitable for applications for which highly transparent materials are required, for example covering lacquers.